Fucking in public is generally considered to be fucking in public whether or not the guys are naked or not. So if you're going to fuck in public, you may as well be fucking naked.
Unless you want to do the slick thing of wearing a raincoat with a slit up the back and dropping your pants below the raincoat. Makes for easy access. Though people may be suspicious why the person behind you is so close behind you and seems to be making a certain recognizable type of thrusting motion. Plus your moans may give it away, so bring a sock to bite on.